1. Field of the Invention
The present invention relates to a semiconductor device, a circuit, a display device using the same, and a method for driving the same, and in particular, it relates to a semiconductor device for which MOS (Metal Oxide Semiconductor) transistors with SOI (Silicon on Insulator) structures, such as polysilicon (polycrystalline silicon) TFTs (Thin Film Transistors), have been integrated, a circuit, a display device using the same, and a method for driving the same.
2. Description of the Related Art
Polysilicon TFTs formed on insulating substrates had once required expensive quartz substrates for high-temperature processing and had been applied to small-sized and high-added-value display panels. Thereafter, a technique for forming a precursor film by a method such as low-pressure (LP) CVD, plasma (P) CVD, or sputtering and then laser-annealing the same for polycrystallization, namely, a technique capable of forming polysilicon TFTs at a lower temperature which allows use of a glass substrate or the like was developed. Moreover, simultaneously, techniques for oxide film formation, microprocessing, and circuit design have also repeatedly made progress, thus consequently, preparation of portable telephones, personal digital devices, and polysilicon TFT display panels for notebook PCs for which peripheral circuits of display panels have been integrated on substrates identical to those of pixels has begun.
As a specific example, provided is an active matrix-type display device disclosed in prior art 1 (Japanese Published Unexamined Patent Application No. 2004-046054). FIG. 1 is a block diagram showing a configuration of a display system of a conventional common liquid crystal display device integrated with a drive circuit described in FIG. 39 of the prior art 1.
Referring to FIG. 1, in the conventional liquid crystal display device integrated with a drive circuit, an active matrix display region 110 for which wiring has been provided in a matrix form and pixels of M rows and N columns have been arranged, a row-wise scanning circuit (scanning line (gate line) drive circuit) 109, a column-wise scanning circuit (data line drive circuit) 3504, an analog switch 3505, a level shifter 3503, etc., are formed on a display device substrate 101 in a manner integrated by polysilicon TFTs.
A controller 113, a memory 111, a digital/analog conversion circuit (DAC circuit) 3502, a scanning circuit/data register 3501, etc., are of an integrated circuit chip (IC chip) formed on a single-crystal silicon wafer, and are mounted outside the display device substrate 101. The analog switch 3505 has an output number equal to the number N of row-wise data lines of the active matrix display region 110. An interface circuit 114 is formed on a system-side circuit board 103.
In addition, some of the conventional liquid crystal display devices with integrated drive circuits composed of polysilicon TFTs are formed in a manner integrated with more complicated circuits such as DAC circuits. FIG. 2 is a block diagram showing a configuration of a display system of a conventional liquid crystal display device with a built-in DAC circuit described in FIG. 40 of prior art 1. In the conventional liquid crystal display device with a built-in DAC circuit, similar to the device of FIG. 1, which does not have a built-in DAC circuit, in addition to an active matrix display region 110 for which wiring has been provided in a matrix form and pixels of M rows and N columns have been arranged, a row-wise scanning circuit 109, and a column-wise scanning circuit 3506, circuits such as a data register 3507, a latch circuit 105, a DAC circuit 106, a selector circuit 107, and a level shifter/timing buffer 108 are formed in a manner integrated on a display device 101.
In this configuration, a controller IC mounted outside the display device substrate 101 can be composed of a memory 111, an output buffer circuit (D bits) 112, and a controller 113, which are all low-voltage circuits or elements, without including a DAC circuit that uses a high voltage. As a result, since an IC can be fabricated without simultaneously using a process for a high voltage required to generate a voltage signal for writing into a crystal, the price can be held down at a lower price than that of the aforementioned IC consolidated with a DAC.
The above-mentioned liquid crystal display devices are low in profile and lightweight. By making the best use of such features, these liquid crystal display devices are loaded on portable information processors.
Furthermore, a liquid crystal display device for which a power supply circuit composed of polysilicon TFTs has been integrated in the periphery of a display region and which has been successfully driven was recently described in prior art 2 (SID (Society for Information Displays) p. 1392, Digest of Technical Papers in 2003). According to the prior art 2, in addition to a scanning line drive circuit and a data line drive circuit including a 6-bit DAC, a power supply circuit composed of a charge pump circuit and a regulator circuit is formed by polysilicon TFTs in the periphery of a display region, and when a single power supply, for example, a 3V power, is supplied to a panel, another voltage necessary in the panel is generated. Therefore, a power supply circuit IC, which had conventionally been required outside the panel, has become unnecessary.
Moreover, in prior art 3 (ISSCC (IEEE International Solid-State Circuits Conference) 2003, Paper 9.4), an example of an 8-bit CPU with a supply voltage of 5V and an operating frequency of 3 MHz prepared by TFTs formed on a glass substrate has been described. The process rule has been provided as 2 μm. As such, the techniques for preparing polysilicon TFT integrated circuits have been remarkably developed, and are currently nearly reaching a level to realize integrated circuits on glass substrates, which were formed on single-crystal silicon wafers about 30 years ago, in 1975, for example.
Based on such a background as this, as is referred to as a “system on glass,” development of a device for which an output function such as a display and an input function such as an image sensor, and peripheral circuits thereof, for example, a memory and a CPU and the like, are integrated on a glass substrate has been advanced.
A polysilicon TFT is generally a MOS-type 3-terminal element provided with a source terminal, a drain terminal, and a gate terminal, and when a circuit is constructed with use of polysilicon TFTs, a circuit configuration thereof can make a reference to a circuit configuration of a so-called bulk MOS integrated circuit, which has been formed with use of a single-crystal silicon wafer.
A circuit configuration and operations of a bulk DRAM (bulk Dynamic Random Access Memory) constructed with use of conventionally known bulk MOS transistors have been described in prior art 4 (“CMOS Integrated Circuit—from introduction to actual use—” authored by Tadayoshi Enomoto), for example. FIG. 3 and FIG. 4 show a DRAM basic circuit and its readout operation and signal waveforms described on page 192 of the prior art 4. Here, of the symbols used in the text and figures of the literature, “D bar” which denotes an inversion of “D” will be displayed, for the convenience of display in a patent document, as “XD” for description.
Referring to FIG. 3 and FIG. 4, a bulk DRAM disclosed in the prior art 4 will be described. First, description will be given of a readout operation when memory contents of a readout cell C1 (upper cell out of the two cells) are “1” with reference to FIG. 3 and FIG. 4. When a precharge pulse φp rises, a bit line pair of D-line and XD-line is set to VD/2. Next, word line WLx (upper line out of the two lines shown) rises and the D-line is raised by ΔV. When φAn reaches a high potential, n-channel MOS transistors (nM1 and nM2) of a latch-type sense amplifier start operation, and the n-channel MOS transistor (nM2) has continuity upon receiving potential of the high-potential D-line so as to lower potential of the XD-line of a low-potential side to 0V. On the other hand, a p-channel MOS transistor side functions in contrast to the n-channel MOS transistor side. Namely, when φAp reaches a high potential, the p-channel MOS transistor (pM1) has continuity upon receiving potential of the low-potential XD-line so as to charge the high-potential D-line until it reaches VD. It is considered that, when memory contents of the cell are “0,” the operation is reverse of the case for reading out “1.”
As such, the minute voltage signal ΔV read out from the memory cell onto the bit line pair is amplified to VD and 0 by the latch-type sense amplifier circuit. In addition, by writing the signal herein amplified to VD and 0 into a capacitance C1 of the memory cell via the bit lines, a refresh operation can be carried out.
Here, the driving method mentioned in the above is called a “VD/2 precharge method,” wherein an absolute value |ΔV| of ΔV is provided as a primary approximation as in the following numerical expression 1. Here, C1 denotes capacitance of the memory cell C1, and C2 denotes parasitic capacitance of the D-line or DX-line.
                                                    Δ            ⁢                                                  ⁢            V                                    =                              C                          2              ⁢                              (                                                      C                    1                                    +                                      C                    2                                                  )                                              ⁢                      V            D                                              (        1        )            
The description in the above is of a configuration and operations of a bulk DRAM constructed using bulk MOS transistors, meanwhile a similar circuit configuration and operations have been known with regard to a so-called SOI DRAM that utilizes single-crystal silicon on oxide films as channels as well, and this has been described in prior art 5 (page 261 of “SOI Design: Analog, Memory and Digital Techniques” authored by Andrew Marshall), for example.
In addition, an example of the foregoing sense amplifier circuit constructed using TFTs has also conventionally been known. For example, according to FIG. 2 and paragraph 0078 of the specification of prior art 6 (Japanese Published Unexamined Patent Application No. 2002-351430), a latch-type sense amplifier with a configuration the same as that of the latch-type sense amplifier shown in FIG. 3 is constructed by use of p-channel and n-channel TFTs.